Organic Letters
Letter
Scheme 4. Possible Reaction Mechanisms
ACKNOWLEDGMENTS
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Support has been provided by the National Science
Foundation: Grant Nos. CHE-1213638 to N.J.K., CHE-
0722547 to K.A.W., CHE-0821487 for NMR facilities at
Oakland University, and CHE-1048719 for LC−MS facilities at
Oakland University.
REFERENCES
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lactone 3 as the trans-diastereomer.2,4 This mechanism is
consistent with the one we have proposed for the formation of
γ-lactones from sulfoxonium ylide, ketenes, and aldehydes in
that both involve enolate 4 as a key intermediate.2,3 Indeed, it
was noted that the same major diastereomer was formed from
the reaction of 2-phenylpropionic acid with vinylsulfoxonium
2b (yield = 62%, dr = 80:20), as was obtained from the three-
component reaction of aminosulfoxonium ylide with isobutyr-
aldehyde and methylphenylketene (yield = 33%, dr = 92:8).2
Alternatively, ylide intermediate 5 could be formed through
conjugate addition of lithium enediolate to the β-position of
vinylsulfoxonium 2 (Mech 2, Scheme 4).9 Protonation of ylide
5 (by lactone/acid/intramolecular proton transfer) followed by
cyclization would provide access to γ-lactone 3. Such a
mechanism could also account for the high trans-diastereose-
lectivity observed if a closed transition state (through Li
chelation) was involved in the conjugate addition step (Scheme
4).10
(9) Lu, P.; Jackson, J. J.; Eickhoff, J. A.; Zakarian, A. J. Am. Chem. Soc.
2015, 137, 656−659.
(10) (a) Oare, D. A.; Heathcock, C. J. Org. Chem. 1990, 55, 157−172.
(b) Kwan, E. E.; Evans, D. A. Org. Lett. 2010, 12, 5124−5127.
In conclusion, we report that the reaction of lithium
enediolates with vinylsulfoxonium salts provides an efficient
and highly diastereoselective route to γ-lactones. This versatile
method complements our recently reported one-pot method-
ology for the preparation of γ-lactones from disubstituted
ketenes in that it mainly provides access to γ-lactones bearing
α- and β-tertiary stereogenic centers. Future studies will focus
on the development of an asymmetric variant of the reported
reaction.
ASSOCIATED CONTENT
* Supporting Information
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S
Experimental procedures, spectroscopic data for all new
compounds, X-ray data for lactone 3a (CIF), and NOESY for
3n. This material is available free of charge via the Internet at
AUTHOR INFORMATION
Corresponding Author
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Notes
The authors declare no competing financial interest.
C
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